Brief Report Loss of B Cell Anergy in Type 1 Diabetes Is Associated With
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Page 1 of 63 Diabetes Brief Report Loss of B cell anergy in type 1 diabetes is associated with high risk HLA and non- HLA disease susceptibility alleles Mia J. Smith1,2, Marynette Rihanek3, Clive Wasserfall4, Clayton E. Mathews4, Mark A. Atkinson4,5, Peter A. Gottlieb3, and John C. Cambier1 1Department of Immunology and Microbiology, University of Colorado School of Medicine, Aurora, CO; 2Department of Microbiology, Immunology, and Pathology, Colorado State University, Fort Collins, CO; 3Barbara Davis Center for Childhood Diabetes, University of Colorado School of Medicine, Aurora, CO; 4Department of Pathology, Immunology, and Laboratory Medicine, The University of Florida College of Medicine, Gainesville, FL; 5Department of Pediatrics, The University of Florida College of Medicine, Gainesville, FL Corresponding Author: John C. Cambier 12800 E 19th Avenue RC1 North, P18-8100 Aurora, CO 80045-2537 Phone: 303-724-8663 E-mail: [email protected] Condensed Title: Genetic associations with loss of B cell anergy in type 1 diabetes Word Count: 2557/2000, Abstract (202/200), Figures (3), Tables (0), References (37/25) Diabetes Publish Ahead of Print, published online January 17, 2018 Diabetes Page 2 of 63 Although B cells reactive with islet autoantigens are silenced by tolerance mechanisms in healthy individuals, they can become activated and contribute to development of type 1 diabetes. We previously demonstrated that high-affinity insulin-binding B cells (IBCs) occur exclusively in the anergic (BND) compartment in peripheral blood of healthy subjects. Consistent with their activation early in disease development, high-affinity IBCs are absent from the BND compartment of some first-degree relatives (FDRs) as well as all autoantibody positive pre- diabetic and new-onset type 1 diabetes patients, a time when they are found in pancreatic islets. Loss of BND IBCs is associated with loss of the entire BND B cell compartment, consistent with provocation by an environmental trigger or predisposing genetic factors. To investigate potential mechanisms operative in subversion of B cell tolerance, we explored associations between HLA and non- HLA type 1 diabetes-associated risk allele genotypes and loss of BNDs in FDRs. We found that high-risk HLA alleles and a subset of non-HLA risk alleles, i.e. PTPN2 (rs1893217), INS (rs689) and IKZF3 (rs2872507), relevant to B and T cell development and function, are associated with loss of anergy. Hence, our results suggest a role for risk-conferring alleles in perturbation of B cell anergy during development of type 1 diabetes. Page 3 of 63 Diabetes Type 1 diabetes (T1D) is an autoimmune disease in which self-reactive lymphocytes destroy insulin-producing pancreatic beta cells. While genetic variation is thought to be the major contributor to risk of developing T1D, environment also plays a contributing role. Together, these factors may impart their effects by compromising maintenance of immune tolerance in T cells and/or B cells, both of which are known to be essential in the pathogenesis of the disorder (1-4). Studies have shown that B cells likely act as antigen presenting cells and autoantibody producers in type 1 diabetes (5; 6). How self- reactive B cells, which are normally silenced in healthy individuals, become activated to participate in this disease is not known. Previous studies have demonstrated that up to 70% of all B cells generated in the bone marrow are autoreactive (7). Autoreactive B cells are silenced by multiple mechanisms. Those reactive with highly avid self-antigens, e.g. cell surface proteins, undergo receptor editing, in which they rearrange their antigen receptor light chains modifying specificity (8). If this process fails to eliminate autoreactivity, cells can undergo apoptosis via a mechanism referred to as clonal deletion (9). Cells reactive with low avidity autoantigens, even if they have high affinity, do not receive signals that are sufficiently strong to induce receptor editing or clonal deletion. These cells mature and proceed to the periphery where they are maintained in a state of unresponsiveness termed anergy. Anergic B cells show evidence of previous antigen exposure including downregulation of surface IgM, elevated basal calcium and activation of negatively regulating signaling circuitry, but are refractory to further stimulation (10-12). Importantly, studies in mice have demonstrated that anergy is rapidly reversed if autoantigen dissociates from the B cell receptor (BCR), suggesting that this Diabetes Page 4 of 63 unresponsive state is maintained by a non-durable, presumably fragile, biochemical mechanism, rather than genetic reprogramming (13). Consistent with this mechanism, inhibitory signaling pathways are upregulated in anergic cells by protein phosphorylation, e.g. SHIP1 and SHP-1, and miRNA regulation of effector expression, e.g. PTEN (14; 15). B cell intrinsic expression of these regulatory phosphatases is required for maintenance of anergy (14). It is likely that additional genetic factors play a role in tuning B cell responsiveness to antigen and maintenance of anergy. Obvious candidates reside among the products of gene alleles that have been shown to confer increased risk of developing autoimmunity. We previously examined the status of insulin-reactive B cells (IBC) in peripheral blood of healthy individuals. We observed that B cells with high-affinity for insulin occur in blood of healthy subjects where they are restricted in the anergic compartment (16). These cells are polyreactive, binding to LPS and chromatin, as well as insulin. Interestingly, they disappear from this compartment in islet autoantibody-positive and recent-onset type 1 diabetes subjects, as well as a portion of healthy first-degree relatives (FDRs) of type 1 diabetes patients (Figure 1 and Supplemental figure 1). Preliminary studies in our lab suggest the disappearance of these cells reflects their relocalization to the pancreas and pancreatic lymph nodes. Specifically, IBC are enriched among B cells in pancreatic islets of type 1 diabetics (Smith and Cambier, unpublished). However, we cannot rule out the possibilities that these cells simply upregulate surface IgM, and thus enter the mature naïve compartment, or do not enter the anergic compartment. Page 5 of 63 Diabetes To better understand what factors contribute to loss of B cells from the anergic compartment of blood early in type 1 diabetes, we explored the correlation between BND frequency among FDRs and high-risk HLA and non-HLA type 1 risk allele genotype. Diabetes Page 6 of 63 RESEARCH DESIGN AND METHODS Subject selection and peripheral blood processing Peripheral blood was obtained with informed consent at the Barbara Davis Center for Childhood Diabetes using protocols approved by the University of Colorado Institutional Review Board. Eligible type 1 diabetes subjects were males or females who met the American Diabetes Association criteria for classification of disease. Autoantibodies against insulin (IAA), GAD, IA-2, and ZnT8 were assayed using radioimmunoassays, as previously described (17). Peripheral blood mononuclear cells (PBMCs) from autoantibody negative FDR (n=103), autoantibody positive pre-diabetes subjects (n=18; identified in the Type 1 Diabetes TrialNet Natural History study), new-onset type 1 diabetes patients (n=21; duration < 12 months), long-standing type 1 diabetes patients (n=21; duration > 12 months), and healthy age/sex matched controls (n=49) were isolated from heparinized blood by Ficoll-Hypaque fractionation. DNA was extracted from the granulocyte layer using the DNA midi kit (Qiagen). Flow cytometric analysis and enrichment of IBCs In order to maintain consistency of gating of flow cytometry data, each subject sample set was analyzed in parallel with an age/sex matched healthy control. The healthy control cells were used to construct gates, which were then copied to the FDR subject cells. Gating for BND cells was based on CD19- T cells and FMO compensation controls. PBMCs were stained in PBS/1%BSA/0.02%NaAzide with human FcR Blocking Reagent (Miltenyi), 0.1 µg/106 cells insulin-biotin, and mouse monoclonal anti-human antibodies against CD19-BV510 (BioLegend), CD27-PerCP or CD27-BUV395 (BioLegend), IgM- Page 7 of 63 Diabetes PE (Southern Biotech), and IgD-FITC (BD Biosciences) or IgD-BV421 (BioLegend) for 20 minutes at 4ºC. After washing, cells were fixed with 2% formaldehyde at 4ºC, followed by incubation with streptavidin-AlexaFlour647 for 20 minutes at 4ºC. Cells were washed, suspended in MACS buffer (PBS/0.5%BSA/2mMEDTA), and incubated with Anti-Cy5/Anti-Alexa647 microbeads (Miltenyi) for 15 minutes at 4ºC. Samples were then passed over magnetized LS columns (Miltenyi), washed 3 times with 2 mL of MACS buffer, and bound cells were eluted with 6 mL of MACS buffer. Flow cytometry was preformed an LSR II (BD) and data analyzed with FlowJo software version 8.8.4. Absolute cell counts were performed using a hemocytometer (Fischer Scientific) to enumerate total lymphocytes. Total B cell numbers were then determined by multiplying the frequency of CD19+ B cells determined by FACS by the total cell count determined by the hemocytometer. Absolute IBC numbers were determined by multiplying the frequency of IBCs in the CD19+ B cell gate by the total B cell count. Absolute IBC BND cells were determined by multiplying the frequency of CD27- IgMlo/- IgD+ cells within the IBC gate by the total IBC cell count. HLA and non-HLA genotyping DNA from FDRs (n=103) and healthy controls (n=49) was HLA genotyped at the Autoantibody/HLA Service Center at the Barbara Davis Center for Childhood Diabetes using established protocols (18). DNA from 60 FDRs was sent to the University of Florida Center for Pharmacogenomics for non-HLA genotyping. The purified DNA was then genotyped on a custom Taqman single nucleotide polymorphism (SNP) genotyping Diabetes Page 8 of 63 array (ThermoFisher). All results from non-HLA genotyping are available in Supplemental Table 1. Statistics Data were analyzed using Prism software (GraphPad Software, Inc.). One-way ANOVA followed by a Bonferroni’s Multiple Comparison post-test was used to determine significance of differences along the five patient groups, defined as P<0.05.